Campylobacter spp. is a leading cause of diarrheal disease among US troops deployed to Thailand for exercise. We investigated the importance of immunological analysis and immune responses against Campylobacter infection in US troops deployed to Thailand. Blood and fecal samples were collected from volunteered soldiers with diarrhea and from healthy controls. Stool culture was performed to identify the pathogens. Campylobacter‐specific antibodies, antibody secreting cells and cytokines were measured. Several bacterial protein fragments in the outer membrane extract of Campylobacter spp., were identified by an immunoblot analysis with plasma and fecal antibodies. Among all of the diarrheal cases, 35% were Campylobacter‐positive. Based on antibody titers in plasma and in fecal extract and antibody secreting cells: 6% of healthy controls, 32% of the Campylobacter culture‐negative diarrheal cases, and 85% of the Campylobacter culture‐positive diarrheal cases were positive for Campylobacter. Our results indicate that the measurement of Campylobacter‐specific antibodies in plasma and fecal extract samples is a good marker of exposure to Campylobacter, and this test may be a useful diagnostic tool for seroepidemiological studies. Elicited antibodies against several bacterial outer membrane protein fragments suggest that these protein fragments are vital in providing protective immunity against Campylobacter.